Most prior art exhaust mufflers comprise parallel tubes supported by transversely extending oval or circular baffles. The assembly of the parallel tubes and transverse baffles is slid within a tubular outer shell having a cross-sectional size and shape conforming to the shape of the baffles. An outer wrapper may then be wrapped about the outer shell to define a double-layer outer wall for the muffler. The double wall construction provided by the outer wrapper is intended to dampen shell ring, which is noise that would be generated by vibrations of a single layer outer wall. A pair of opposed end caps are then mechanically connected to the tubular outer shell and the outer wrapper to enclose the opposed longitudinal ends of the muffler. The end caps are provided with inlet and outlet apertures to permit the flow of exhaust gas through the muffler. With this prior art construction, a plurality of chambers are defined within the muffler. In particular, each chamber will be defined by the outer shell of the muffler and either two baffles or one baffle and an end cap. The tubes of these typical prior art mufflers are located and configured to permit communication of exhaust gases with the chambers defined inside the muffler. For example, the tubes may be provided with perforations, louvers or apertures which permit the flow or expansion of exhaust gases into a chamber. In other situations, a tube may terminate within a chamber to permit the crossflow of exhaust gases into another tube or to permit the dampening of certain low frequency sounds within an enclosed chamber.
The above described typical prior art muffler generally attenuates noise adequately. However, these prior art mufflers are undesirable in that they include a large number of separate components which must be manufactured and assembled in labor intensive manufacturing processes. These prior art mufflers also typically are undesirably heavy. Additionally, the above described prior art mufflers with tubular outer shells invariably have a generally rectangular plan view configuration. This limitation on the shape of the prior art muffler has made it extremely difficult to design the muffler to fit within the limited available space on the underside of a vehicle.
The prior art also includes mufflers formed at least in part from stamp formed components. For example, U.S. Pat. No. 4,396,090 which issued to Wolfhugel on August 2, 1983 shows a muffler having a pair of internal plates stamp formed to define pairs of opposed channels. The internal plates are assembled to one another such that each pair of opposed channels defines a tube therebetween. The internal plates defining the channels are disposed within a conventional wrapped outer shell as in the above described prior art conventional muffler.
The prior art also includes mufflers consisting of only two opposed shells which are stamped to define a convoluted array of tubes and chambers through which the exhaust gas may travel. Mufflers of this general type are shown in U.S. Pat. No. 3,176,791 which issued to Betts et al on April 6, 1965 and U.S. Pat. No. 3,638,756 which issued to Thiele on February 1, 1972.
The prior art further includes mufflers formed from more than two stamped components. Mufflers of this general type comprise a pair of internal plates stamped to define opposed channels such that when the plates are disposed in face-to-face relationship, the juxtaposed channels define tubes between the plates. Selected portions of these tubes have been provided with arrays of perforations, louvers or the like extending therethrough to permit the expansion of exhaust gases therefrom. These prior art mufflers further comprise a pair of stamp formed external shells which are disposed around the internal plates to define a chamber surrounding portions of the formed tubes having perforations, louvers, apertures or the like extending therethrough. Certain of these prior art mufflers further have included separate baffles extending between the internal plates and the external shell to define a greater number of chambers within the muffler. Examples of mufflers of this general type are shown in British Patent No. 632,013 which issued to White in 1949; British Patent No. 1,012,463 which issued to Woolgar on December 8, 1965; Japanese Published Patent Application No. 59-43456 which was published in 1984; U.S. Pat. No. 4,132,286 which issued to Hasui et al on January 2, 1979 and U.S. Pat. No. 4,415,059 which issued to Hayashi on November 15, 1983.
The above described prior art stamp formed mufflers have not received significant commercial success in the United States. In particular, these prior art stamp formed mufflers have generally conformed to the same rectangular plan view configuration of the conventional prior art mufflers with wrapped outer shells. As a result, the above described stamp formed mufflers have offered no advantage in packaging convenience. Additionally, the above described prior art stamp formed mufflers have functionally relied substantially entirely upon expansion chambers for attenuation of noise. However, mufflers relying exclusively upon expansion chambers generally fail to attenuate certain low frequency noise. These residual low frequency noises often have been acceptable on certain European cars. However, the residual low frequency noise associated with the above referenced prior art stamp formed mufflers has generally not been accepted in the United States.
Recently several significant advances have been made in stamp formed mufflers. In particular, U.S. Pat. No. 4,700,806 which issued to Jon Harwood on October 20, 1987 shows a muffler formed from stamp formed components and providing the combination of at least one tuning tube and at least one low frequency resonating chamber. Mufflers manufactured in accordance with U.S. Pat. No. 4,700,806 have proved extremely successful in attenuating both high frequency and low frequency noise, and have achieved very substantial commercial success in a short period of time. Other improvements relating to stamped mufflers are shown in U.S. Pat. No. 4,736,817 which issued to Jon Harwood on April 12, 1988; U.S. Pat. No. 4,759,423 which issued to Jon Harwood et al on July 26, 1988; U.S. Pat. No. 4,760,894 which issued to Jon Harwood et al on August 2, 1988 and U.S. Pat No. 4,765,437 which issued to Jon Harwood et al on August 23, 1988. All of the above described Harwood patents are assigned to the assignee of the subject invention, and the disclosures thereof are incorporated herein by reference.
All of the above described stamp formed mufflers which comprise arrays of formed tubes have the tubes defined by a pair of opposed generally planar plates having channels formed therein. Thus, with the possible exception of the inlet and outlet to the muffler, the central axes of the formed tubes have been generally planar. Additionally, those prior art mufflers formed from four separate plates have generally shown the tubes being defined by the two formed internal plates and the chambers being defined sustantially by the two external shells.
As noted above, mufflers have a tendency to produce shell ring, which is attributable to vibrations in the walls of the external shell of the muffler. The conventional mufflers avoid the shell ring by providing a separate outer wrapper to dampen the vibrations of the tubular shell of the muffler. The provision of the outer wrapper, however, imposes substantial weight and cost penalties. The prior art stamped mufflers that have been marketed in Europe over the years have largely tolerated higher noise levels, and therefore have generally not addressed the issue of shell ring. The problems associated with shell ring have been addressed in co-pending U.S. Pat. Application Ser. No. 227,807 which was filed by the inventors herein on August 3, 1988 and is entitled Stamp Formed Muffler With Reinforced Outer Shell. Despite the advantages of the construction shown in co-pending Application Serial No. 227,807, it is desired to provide further options for the construction of mufflers that will substantially eliminate shell ring.
It is also an object of the subject invention to provide a stamp formed muffler with a nonplanar array of tubes.
It is another object of the subject invention to provide a stamp formed muffler wherein the tubes are defined between one internal plate and one external shell.
It is an additional object of the subject invention to provide a stamp formed muffler wherein an internal plate having channels therein is secured to the external shell to reinforce the external shell and thereby attenuate shell ring.
Still another object of the subject invention is to provide a stamp formed muffler wherein the chambers are generally internally disposed, and wherein the tubes are disposed adjacent the external shells.
A further object of the subject invention is to provide a stamp formed muffler with a nonplanar array of tubes and with a generally planar lower shell to conform to specified sight lines and aerodynamic planes for the vehicle.